1. FIELD OF THE INVENTION
The present invention relates to a crankshaft structure of two-cycle internal combustion engine for a vehicle such as motorcycle or the like.
2. DESCRIPTION OF THE PRIOR ART
In a conventional two-cycle internal combustion engine, for example, of the type having two cylinders disposed in parallel with each other, the crankshaft structure is arranged such that in the axial direction of the crankshaft are disposed a crank web for one cylinder, a first bearing, a sealing member such as labyrinth seal, a second bearing and a crank web for another cylinder in the mentioned order, in other words, two bearings are disposed on both sides of the midst sealing member on a crank journal portion. This arrangement increases the axial length of the crank journal portion and therefore leads to a large total width of the engine, causing the mounting position of the engine on a body of vehicle, such as a motorcycle, to be shifted upwardly for ensuring a desired banking angle.
With this conventional arrangement, more dead space is produced around the crank journal portion to increase the volume of crank chamber, thereby deteriorating the primary compression ratio. For solving this problem, a measure may be taken that the total width of engine is reduced by shortening the axial width of each of the crank webs, however, this undesirably results in shortage of the length of a supporting part of the crank web as fitted with the crank journal portion.